NOW THAT I'VE BARED MY SOUL, at least insofar as what's important to me in a touring bike, let's talk about some of the experience I gained during a month of loaded, self-supported touring on my Bike Friday.

Wheel size and tires

The first thing to cover has to be the tires.  I had the worst run of luck you could imagine: something like eight or ten flats, a bead failure, and another structural failure of the innards of the rear tire after I hit a pothole very hard.  The tires were brand new at the start of the tour so it wasn't a matter of having started with nearly worn-out rubber.  They were a brand and model that is ostensibly high-quality, made for touring, that I and many others have had very good results with over time.

I chose them because I've used them, with reasonable success, for many years both on Odysseus and on our Bike Friday tandem and because the consensus of Public Opinion is that they're among the best options available.  They are also very nearly the only option available in the size I need.

Both bikes (NWT and tandem) have 20-inch (406) rims, a key feature in their mission of being bikes that are relatively easy to travel with.  They disassemble and fold, fitting into regular-size suitcases that do not provoke awkward questions at airline luggage check in counters.  However, it has the side effect of dramatically narrowing the field of candidate tires.  

The lesson I took away from my saga was not so much that the tires were in and of themselves a poor choice, but rather they were one of only two options I was aware of.  Plus, as a less-than-common size, there are fewer possible suppliers.  (The shops I checked in carried either no tires in 406 size, or only a couple knobby models intended for kids mountain bikes; they are too wide to fit the space between the chain stays on my bike.)  In the age of COVID and supply chain disruptions, along with a general ongoing shakeout and elimination of small independent bike shops, oddball stuff is simply nearly impossible to find on the shelf.  Even large national brands no longer stock 20 inch tires, or even 20 inch tubes with Presta valves.

Future Bike will have either 26 inch or 700c wheels.  That will, I hope, provide a much wider range of options in terms of brand, model, and feature.  It should also greatly broaden the number of outlets where I could obtain replacements (including replacement inner tubes, by the way), even if they are just temporary "limp along until I find what I want" interims.

The tires and rims will be traditional tubed models (still with Presta valves, though), not the tubeless ones that are seemingly finding their way (back) into vogue at the present.  I have an impression, perhaps unfounded and misguided, that the current tubeless revolution is a passing fad.  Even if it isn't, it's a pretty safe bet that tubed tires will continue to be around, and widely available, for the entirety of the time I intend to own and ride Future Bike, so it "feels like" a safe choice to make to stay with that option.

Gearing and rear hub

It's less than clear whether my fairly low average speed (I typically covered ten or fewer miles in an hour) was due in part or in whole to the small wheel size (and the perceived "inefficiency" that goes with them).  What I can say with certainty is that I never had a problem finding a gear combination that was too high so it's not simply a matter of running out of gears.  The gearing on the bike (and some of the components) was specifically selected to compensate for the smaller wheels.

I also can't comment on whether I was working any harder on this bike to achieve a particular level of performance than I would have done on a more traditional bike.  I simply have no means to compare, let alone ascribe any difference to a particular factor or factors.  But I do know that I was slow.

The way I got the gears that compensate for the smaller wheels was by selecting Shimano's Capreo hub and cassette.  Although that hub has performed well over its life (I have no complaints about it, per se) it is a choice I have come to regret. Well, "regret" may be too strong a term, but it's a choice I'd make differently now.

For one thing, they're long since out of production.  That means that replacement parts are, at best, going to be rare and hard to find (and correspondingly expensive) or they're simply going to be unobtainable at any price.  I managed to find a replacement cassette last winter, at a cost of about $150.  Ouch.

For another, it's a design proprietary to Shimano.  There is a Chinese company that still manufactures a compatible equivalent, but again they're a sole-source and I'd be at their mercy in the event of a problem.  (Assuming, of course, that I could even find a supplier who would and could provide it to the U.S. market to begin with.)

In either case, the odds that a small-town, relatively limited bike shop would even know what they were looking at, let alone be able to service, are fairly low.  (Oh, it also takes a Capreo-specific tool to remove the lock ring, meaning I have to carry one because it's unlikely that a shop will have one.)

Finally, Shimano never offered a version of the Capreo hub that is disc-brake compatible.  Given that disc brakes are very high on the must-have list, the Shimano-branded Capreo hub would be a non-starter under any circumstance.  Their Chinese successor does make such an item but I've already detailed the reasons why I won't be selecting that.  

So, Future Bike will be set up with readily-available disc-brake hubs and either 26 inch or 700c wheels.

Brakes

I've never owned a bike with disc brakes.  Future Bike will have them.  Why?

Rim brakes put heat into the rims.  That heat is transferred by contact into the tire and inner tube.  Ideal gas laws say that an increase in temperature of a gas causes a corresponding (and proportional) increase in the pressure and/or volume of the gas.  In a bicycle tire inflated to its intended pressure the volume is essentially held constant by the tire, so all of the heat generated by braking is translated to increased pressure in the inner tube.

If the rim gets hot enough, and stays that way long enough, the higher pressure in the inner tube can blow the tire off the rim.  Given that prolonged heavy braking most typically occurs on a steep or high-speed descent, the consequences of blowing a tire off the rim are potentially catastrophic.  Add to that the fact that more braking occurs in the front wheel than the back.  Blowing the front tire off the rim can result in an instantaneous loss of steering.

That's BAD.  VERY BAD.  Especially if you're doing 30+ miles an hour on a narrow winding mountain road with no shoulder, perhaps no guard rail or containment wall, and a long steep plunge into the valley immediately next to the road.  (I wouldn't like to smash into a stone retaining wall at that speed, either.)  Or if there's oncoming traffic you might find yourself unable to stay on your side of the road.  Even if you don't actually crash and convert yourself to a smear of hamburger on the road surface, nothing good comes of it.

Lest you think I'm overstating the possibility of a blowout, I'll tell you this: it has happened to me, once. Amazingly, and equally fortunately, I didn't crash, plunge off a mountainside to my death, or careen wildly into the grill of an oncoming semi truck.  But only because I was very, VERY lucky.  It's not a position I want to put myself in, ever again.

As a secondary, and relatively trivial and minor consideration, rim brakes also eventually wear out the rims against which they press.  I've twice had to replace wheels when the rims failed after several years of use.  It happens faster, of course, when conditions include extensive riding on wet, gritty surfaces and / or lots of riding with heavy loads that require correspondingly hard application of the brakes.

I wish to avoid both of these things, so I'm going to have Future Bike built with disc brakes.

Disc brakes aren't perfect, of course.  They're notorious for squealing when applied, and equally for being quite finicky to adjust.  Some designs, at least, include small parts that keep the brake pads in place, and which can easily be lost.

They have their own heat issues too: if you get the discs hot enough they can (and do) warp.  The clearance between the rotor and the brake pads is generally quite small, so a warped rotor is at least inconvenient because it'll rub on the pads.  It may be warped so much that the wheel simply won't turn any longer, rendering the bike immobile until the damaged rotor is replaced.

Purely hydraulic braking systems have a further set of potential liabilities.  The fluid can overheat during prolonged braking, causing the brake to fail until it has cooled down.  Depending on the brake design, the failure can either render the brake inoperative ("Look ma!  No brakes!") or lock it in the fully engaged position ("Look Ma!  I can't move!").

The fluid level also has to be properly managed and topped up from time to time. And of course, loss of fluid means loss of braking ability.  So does air in the system.

Mechanical disc brakes, in their earlier incarnations at least, didn't provide as much braking force as their hydraulic peers.  I think that has changed by now, but it's something I need to look into.

There's at least one design that mixes the two.  The brake pistons are hydraulically actuated, but the hydraulic part is in a sealed unit that is connected to the brake lever with a traditional wire brake cable.  At least on the face of it, this seems like a good compromise.  But again, I need to learn more.

Shifters

Odysseus has indexed bar end shifters.  This was a choice I made at the time I bought it, and one I will probably make again.  Scout, his predecessor, had friction-only downtube shifters.  If I thought I could get them, I'd consider going that route again.  But convertible bar end shifters are a decent alternative.

For all that they are convenient, I shy away from integrated brake and shift lever components on a touring bike.  They're more complex than bar end or downtube shifters, and more delicate.  They cannot be set to operate in friction mode, meaning that if I were forced by circumstance to change from, say, a 10 speed cassette to an 8 or 9 speed model, I'd have to change the brake and shift levers too.  

Whether they are integrated with the brake levers or a separate mechanism, indexed shifters are not all created equal.  Different brands have different "pull ratios" and are not interchangeable.  I know this to be true because I once attempted to put a Campagnolo derailleur on a bike equipped with Shimano shifters and cassette.  The result was horrible, unusable.  Shifting was uncertain, and the chain skipped more than a truant skips school because it wasn't correctly positioned.  Reverting to a system where all the parts were of the same manufacture and component group solved the problem.

Even when everything is the same brand there are potential compatibility problems.  An 8 speed cassette requires a different amount of cable pull than a 9, 10, 11, or 12 speed.  The shifters you use must correspond to the cassette in use, and to some degree the derailleurs must as well.

All of this can be avoided using friction shifters, because of course the rider has complete control over how much the lever is moved, which in turn directly moves the cable by a corresponding amount.  Yes, there's more trial-and-error involved, and the shifting is likely to be a bit sloppier and not lightning-quick and precise, but what would you rather have: a delicate finicky system that works pretty well when everything is as the designer intended but which has limited options for field repair, or a less-advanced system that can at a pinch be changed to support nearly anything you throw at it?

I want to be able to shift in friction mode rather than indexed mode for another reason.  Every indexed shift system I've ever used has ultimately gotten very finicky and difficult (for me) to adjust.  I commonly have to shift by two clicks in order to change by one gear, or I have to skip past the gear I want then shift again to get to it.  With friction levers, I know by experience and feel exactly how far to move the lever.

Friction mode also provides infinite adjustability for "trim" adjustments, which indexed shifting does not.  As the chain line moves during gear changes, it is often necessary to make very small changes to the position of the front derailleur in particular, to eliminate the chain rubbing on the inside of the derailleur cage.  That's just a lot easier to do with a friction setup than with indexed, and definitely easier when the shifters are not part of the brake levers.

Future Bike will have bar end shifters, probably.  And they'll be switchable between indexed and non-indexed mode.

Cranks and bottom bracket

Odysseus came with a Shimano Tiagra two-piece triple crank and sealed cartridge bottom bracket.  There's nothing wrong with them, except that the spline that attaches the crank to the bottom bracket is Shimano's proprietary design.  

That puts me at the mercy of Shimano- a company notorious for changing their designs year over year, ensuring that nothing new is backward compatible with anything they've previously made- when it's time for maintenance and replacement.  WHEN, not if, they choose to make my equipment obsolete it will not be serviceable, only replaceable.  Maybe.  In some cases, the stuff they make is so completely integrated into a bike's design that the only viable solution is to replace the entire bike.  Ugh.

This is, by the way, not unique to Shimano.  It seems to be a cancer spreading throughout the bike industry.

Thanks, but NO.  I'll pass.

Future Bike will be built with a crank and bottom bracket that do not lock me in to a single manufacturer for replacement, and that do not necessitate scrapping the bike to make a change or replace worn out parts.

Speaking of cranks (no, not me but you're right), I want nothing to do with the "compact double" crank that features one quite large and one quite small chainring.  The step between them is too great.  A difference of 10 to 12 teeth is all I want.  A 53/36 or 53/34 is like stepping off a cliff.  50/40/30, or 48/36/24 is more like it.  Odysseus's chain rings are 50/39/30.  I'd have preferred a slightly smaller granny ring but didn't really object to what I had, especially when coupled with the cassette it is mated to.

I don't need a gargantuan big ring for a loaded tourer.  I'm not built for speed; the bike doesn't have to be, either.

Future Bike will have a triple crank.  Ideally the granny ring will have between 24 and 28 teeth; the big ring no more than 50.

Cassette

Odysseus has a 9 speed cassette, 9-10-11-13-15-17-20-23-26.  I used them all on my tour, most often finding myself riding the 50/20, 50/17, 50/15, 39/20, and 39/17 combinations on more-or-less level ground and not fighting a headwind.

On a bike with larger wheels cogs of 9, 10, and arguably even 11 teeth are ridiculously small, and 26 is nowhere near big enough for clawing up a long and/or steep incline.  Future Bike will have a cassette with 9 or at most 10 cogs, and something in the 12-32 (or bigger) range.  11 and  12 speed cassettes, and their correspondingly narrower chains, just "feel" like they're too light-duty to do the job over the long haul.

Frame material

Future Bike will be made of either steel or titanium.  If steel it'll be Reynolds, Columbus, or similar double-butted tubing, not straight-gauge material.

No carbon fiber.  It's just not suitable for the rough life a touring bike leads.